Nonflammable electrical cable

ABSTRACT

Nonflammable electrical cable resistant to combustion under current overload conditions. The cable conductor is constituted by one or more composite metal strands. Each strand has an aluminum base core clad with copper and has an outer layer of silver, nickel or tin. The conductor is wrapped with flexible fire-resistant insulating material and the facing areas of the wrapping are sealed with an adhesive which is kept out of contact with the conductor. When subjected to a current overload in an oxygen atmosphere the strand fuses, thereby interrupting the current, before either the insulating material or the adhesive can ignite.

United States Patent Nye NONFLAMMABLE ELECTRICAL CABLE Inventor: EugeneA. Nye, Yorba Linda, Calif.

La Barge, Inc., St. Louis, Mo,

March 10, 197] Assignee:

Filed:

Appl. No.:

References Cited Primary ExaminerE. A. Goldberg Attorney-Koenig,Senniger, Powers and Leavitt 5 7 ABSTRACT Nonflarnmable electrical cableresistant to combustion under current overload conditions. The cableconductor is constituted by one or more composite metal strands. Eachstrand has an aluminum base core clad with copper and has an outer layerof silver, nickel or tin. The conductor is wrapped with flexiblefire-resistant insulating material and the facing areas of the wrappingare sealed with an adhesive which is kept out of contact with theconductor. When subjected to a current overload in an oxygen atmospherethe strand fuses, thereby interrupting the current, before either theinsulating material or the adhesive can ignite.

10 Claims, 3 Drawing Figures BACKGROUND OF THE INVENTION In the designof high performance aircraft and space vehicles, one of the moredifficult problems is the provision of electrical systems which presentminimum hazard when the vehicle is in operation. Electrical systems forboth power and signal purposes are essential to each of the variousvital functions of the vehicle, including propulsion, directionalcontrol and guidance. As a consequence, electrical energy must betransmitted from the electrical power sources to a multitude of pointslocated throughout the vehicle.

To insure the safety of the vehicle during operation, the electricaltransmission equipment must be secure against short-circuiting or othermisdirection of electrical energy and against fire hazards under bothnonnal and current overload conditions. Thus the electrical conductor ofthe transmission equipment must be insulated in a manner which preventscurrent leakage to the surroundings and exposure of the surroundings toexcess temperatures, even when the conductor is seriously overloaded.Moreover, the insulating material itself must be resistant to combustioneven when exposed to the temperatures to which the conductor rises whenoverloaded.

Electrical cable which has been available heretofore has not proved tobe flame resistant under all the conditions to which it is exposed inmodern aircraft or spacecraft. The atmosphere in a space vehiclenormally consists of 95 percent or more by volume oxygen. Thecombustibility of almost all materials is much greater in such anatmosphere than it is in air, which contains only about 20 percentoxygen. Thus, even the most flame-resistant cable insulation materialsknown will burn when exposed to such an atmosphere at the temperaturesto which conventional electrical cable rises during an overload.

Among the best flexible cable insulation materials presently availableare fluorinated ethylene propylene resin (sold under the tradedesignation FEP Teflon" by E. I. DuPont de Nemours and Company) and apolyimide resin (sold under the trade designation Kapton by E. I DuPontde Nemours and Company). A high performance cable which has beencommercially available and which has been used in the electrical systemsof spacecraft consists of a copper conductor surrounded by an insulatingsheath of PEP Teflon," the latter in turn being surrounded by a dipcoating of polyimide film. Though quite satisfactory under normalservice conditions, this cable has not proved to be flame resistant whenexposed to an oxygen-rich atmosphere under electrical current overloadconditions. The inability of this cable to withstand such conditions hasbeen demonstrated by a standard test developed by the NationalAeronautics and Space Administration at the George C. MarshallSpaceflight Center (Specification llA, Jan. 12, 1970). In this test, asample of insulated wire or cable is placed in a chamber whoseatmosphere contains 95 percent by volume oxygen at the operatingpressure of a spacecraft, i.e., about 6.5 psia. After the cable samplehas been allowed to soak in the oxygen atmosphere for a period ofminutes, a current is applied to the sample by means of an external d.c.electrical power supply. The initial test current is 5-20 amps. belowthe nominal fusion current of the cable conductor, depending on the sizeof the wire tested. If ignition is not obtained within one minute of theapplication of current, the current is raised in 5- amp. steps at oneminute intervals until the conductor fails or ignition occurs. Whensubjected to this test, the aforementioned cable has burned, asevidenced by the emission of fumes and smoke, before the fusiontemperature of the conductor has been reached, despite the presence ofthe external sheathing of polyimide material.

A substantial amount of research has been conducted by numerous workersin the art in an effort to provide a nonflammable electrical cable foruse in aircraft and spacecraft which can survive the NASA tests. Priorto the present invention, however, it is believed that none of theseefforts have been successful. Numerous insulating materials andcombinations thereof have been tried with uniformly unsatisfactoryresults. The various insulating materials which have been unsuccessfullytested on copper conductors include all types of fluorocarbon tapes andextrusions, including fluorinated ethylene propylene resin (sold underthe trade designation FEP Teflon" by E. I. DuPont de Nemours andCompany), tetrafluoroethylene resin (sold under the trade designationTFE Teflon by E. I. DuPont de Nemours and Company) and poly vinylidenefluoride (sold under the trade designation Kynar by the PennwaltCorporation); tapes and braids of glass wool fibers and Kapton; andvarious combinations of these insulators including combinations ofKapton and glass fibers.

To insure against the possibility of fire generated by a currentoverload on any of the cables which have been commercially availableheretofore, elaborate precautions are necessary if the cable is used inan oxygen atmosphere. One accepted approach is to encase the cable inablative material and house the resulting structure in aluminum channelspartitioned at frequent intervals to isolate various sections of thecable from one another. These two measures serve to isolate a portion ofcable whose insulation has started burning and to impede access ofoxygen to a site of combustion. Though reasonably effective, thesemeasures are not only expensive in themselves but, more seriously,occupy space and add a substantial amount of weight to a spacecraft oraircraft, thus severely reducing its payload. A critical need hasexisted in the art, therefore, for an electrical cable which isnonflammable under overload conditions in an oxygen atmosphere andwhich, consequently, does not require the use of elaborate space-wastingand weight-wasting measures to avoid the serious hazards whichflammable-type cables otherwise present.

SUMMARY OF THE INVENTION It is an object of the present invention,therefore, to provide a high performance electrical cable which isnonflammable under overload conditions even in an oxygen environment. Itis a particular object of this invention to provide such a cable whichcan be subjected to the sever NASA test conditions without burning,fuming or smoking. A further object of the invention is to provide sucha cable which possesses advantageous mechanical and electricalproperties. Other objects will be in part apparent and in part pointedout hereinafter.

In substance, the present invention is directed to nonflammableelectrical cable, resistant to combustion under current overloadconditions in an oxygen atmosphere, comprising a composite metal strandand an outer wrapping constituted by a flexible fire-resistantinsulating material. The composite strand comprises an aluminum baseconductor core, an annular cladding of copper metallurgically bonded tothe surface of the aluminum base core, and an annular coating of a metalselected from the group consisting of silver, nickel and tin overlyingthe outside surface of the copper cladding. The wrapping of filminsulation has facing areas with adhesive therebetween for sealingpurposes, but the adhesive is entirely out of contact with the compositestrand. The cable is resistant to combustion when subjected to a currentoverload in an oxygen atmosphere with the composite strand being fusedand the current being interrupted before ignition of the insulatingmaterial or the adhesive.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged transversecross-sectional view of the cable of the invention;

FIG. 2 is a plan view illustrating a preferred form of the filminsulation wrapping; and

FIG. 3 is a plan view showing another alternative form of the wrapping.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Unlike the electrical cableswhich have hitherto been employed in the electrical systems of highperformance aircraft and spacecraft, the cable of the present inventionis resistant to combustion even under current overload conditions in anoxygen atmosphere. More particularly, the cable of this invention doesnot support combustion when tested to failure in accordance with NASAsGeorge C. Marshall Spaceflight Center test (Specification 101A, datedJan. 12, 1970). Thus, the cable may be used in oxygen atmosphereswithout the elaborate and expensive precautions and resultant reductionin payload which are required when prior art cables are used. In itspreferred embodiment, the cable of the invention possesses advantageousmechanical properties which satisfy the requirements for utilization ofthe cable in high performance aircraft and spacecraft. These propertiesare preserved during sealing of the insulation by careful control oftemperature conditions in the sealing oven. The cable also possessesoutstanding electrical properties and may be utilized in essentially anypower or signal service without short circuiting, current leakage orexcessive power consumption. Among particular applications in which thiscable has been found highly useful is shielding against radio frequencyinterference and electromagnetic interference.

The novel and unique combination of four essential design principlesprovides the flame resistance of the cable of this invention in anoxygen atmosphere. First, an insulating material such as polyimide or anamidemodified polyimide is used which is resistant to combustion at veryhigh temperatures. Second, the aluminum core conductor, which is usedinstead of conventional copper fuses at a temperature on the order of660 C., far below the l,O83 C. fusion temperature of copper. Theresultant interruption of current, which takes place very quickly oncethe fusion current is reached or exceeded, prevents the insulation fromreaching a temperature at which it can ignite. The thermal insulatingproperties of the insulation contribute to rapid fuse action by impedingdissipation of the heat generated on overload. Third, the adhesivematerial, which normally has an ignition point well below that of theinsulation, is kept out of contact with the conductor strand, beingseparated therefrom by at least one layer of the insulation. Inconjection with the quick fuse action of the core, this preventscombustion from arising with the adhesive. By contrast, conventionalcables heretofore available have commonly included a sheathing ofpolytetrafluoroethylene, or similar materials having softening pointsand ignition temperatures in the range of the adhesives, in directcontact with the conductor. Fourth, the use of a wrapping of insulationinstead of an extruded sheathing provides a more uniform thickness ofinsulation, free from holidays or other defects which occasionally allowmoisture leakage or current leadage in conventional cable. Wrappedinsulation is also generally more flexible than extruded sheathing andis thus more resistant to cracking under conditions of flexure.

Referring to FIG. 1 of the drawings, the novel cable of this inventionhas an aluminum base conductor core 1 which is clad with an annularlayer of copper 3. The copper cladding is in turn coated with an annularlayer 5 of either silver, nickel or tin. The copper cladding providesdesirable termination properties not otherwise possessed by aluminumconductors and the outer coating of silver, nickel or tin furtherenhances the termination properties and provides corrosion resistance.As FIG. 1 shows, the cable preferably includes a plurality of compositemetal strands bundled together inside the insulation. The insulation isconstituted by a wrapping 7 of an insulation material such as polyimideor amidemodified polyimide tape, with an adhesive 9 lying between facingareas of the insulation wrapping for purposes of sealing the insulation.

Diflerent arrangements of the insulation are shown in FIGS. 2 and 3.FIG. 2 shows a preferred embodiment of the invention in which two ormore individual layers of insulation tape are helically wrapped aroundthe conductor with a layer of adhesive lying between the two layers ofinsulation. Such an arrangement is also indicated in FIG. 1.Alternatively, of course, a single layer. of tape may be helicallywrapped around the conductor, with the trailing edge of each wraplapping the leading edge of the preceding wrap and a layer of adhesivematerial lying between the facing areas thus presented to form a helicalseam. FIG. 3 shows another embodiment in which the longitudinal centerline of the tape is oriented parallel to the longitudinal center line ofthe conductor with one edge of the tape lapping the opposite edge in asingle longitudinal seam which is also parallel to the center line ofthe conductor. The seam of FIG. 3 is formed by a layer of adhesive lyingbetween facing areas of the tape. In each embodiment,

the adhesive material is kept out of contact with the conductor, beingseparated therefrom by at least one layer of the film insulation tape.

The composition of the aluminum base core is not critical insofar as thenonflammability characteristics of the cable are concerned. Thus,essentially any aluminum base alloy whose melting point is on the orderof that of aluminum will provide the fuse action which protects againstcombustion of insulation materials such as polyimide or amide-modifiedpolyimide. However, because of the mechanical and electrical propertieswhich are desirable in an electrical cable adapted for use in highperformance aircraft or spacecraft, it is preferable that the aluminumbase core be constituted by an alloy containing between about 0.07percent and about 0.65 percent by weight iron, up to about 0.12 percentby weight silicon, up to about 0.03 percent by weight magnesium, betweenabout 0.01 percent and about 0.03 percent by weight manganese, betweenabout 0.02 percent and 0.04 percent by weight copper, and between about0.006 percent and about 0.01 l percent by weight boron with no more than0.001 percent by weight each of titanium, vanadium, nickel or chromium.The presence of the indicated proportions of iron is especiallyimportant in increasing the tensile strength of the aluminum alloy.Among the aluminum alloys whose compositions fall within the aboveindicated ranges may be mentioned the alloys sold under the tradedesignations EC Aluminum No. 1, EC Aluminum No. 2, CK76" and EC AluminumNo. 3 by the Aluminum Company of America, and the alloy sold under thetrade designation Triple E" by the Southwire Company. The compositionsof these alloys and their associated physical properties are shown inTable I. CK-76 and Triple E are particularly preferred alloys for theconductor core.

The copper cladding constitutes between about 12 percent and aboutpercent by volume of the composite metal conductor strand and ismetallurgically bonded to the aluminum base core. A number ofconventional methods may be employed to provide a metallurgical bond ofcladding to the aluminum conductor core. Among such methods may be notedhotdipping, flame-spraying, electroplating, or solid-phase bonding (asdescribed in U.S. Pat. Nos. 2,691,815 and 2,753,623).

Copper-clad aluminum alloy rod stock, from which the conductor may beproduced by conventional wiredrawing techniques, is commerciallyavailable. Such stock having a diameter of approximately five-sixteenthsinch, for example, is available from Texas Instruments Incorporated. Bya series of conventional drawing and annealing steps the rod stock maybe drawn to any convenient gauge. Preferably the stock is drawn to adiameter corresponding to between 8 and 40 A.W.G. Strands of this sizemay be conveniently woven into a cable bundle having a relatively highdegree of flexibility. Where there are no narrow radius bends in thecable as installed or where no significant flexure in use isanticipated, larger diameter strands may be used. In the latter case abundle of strands may be unnecessary, and the conductor may beconstituted by a single composite metal strand.

As indicated above, size reduction of copper-clad rod stock may beaccomplished by conventional techniques to produce a finished strandhaving the desired mechanical and electrical properties. For use in highperformance aircraft and spacecraft, the finished strand should have atensile strength of at least about 9,000 psi, an elongation of not lessthan about 8 percent and a conductivity of not less than about 60percent I.A.C.S. (conductivity relative to conductivity of copperconductor of same cross section). As indicated in Table I, the preferredaluminum base conductor core materials have properties which aresubstantially superior to these minimums. During size reduction of thecopper-clad rod stock, the ratio of copper volume to total volumeremains substantially constant. Thus the volume of copper produced onthe finished conductor strand can be predetermined by cladding the rodstock with that proportionate volume of copper.

The annular layer of nickel, silver or tin is preferably applied to thecopper-clad aluminum base stock prior to the drawing operation, thoughsilver or tin may be applied after drawing if desired. A silver or tinlayer may be provided by hot-dipping, while a layer of nickel must beapplied by extrusion. Copper-clad aluminum rod having an annular outerlayer of nickel is commercially available from Texas InstrumentsIncorporated and is sold by it under the trade designation DFE3.

Regardless of which metal is used for it, the outer layer should have athickness of at least about 40 microinches after drawing. As with thecopper cladding, the annular cross-sectional area of the silver ornickel coating is reduced proportionately to the reduction of the corearea during drawing. The thickness of the outer coating may then besimilarly predetermined.

The wrapping of insulation is preferably constituted by a film ofpolyimide resin (sold under the trade designation Kapton by E. I. DuPontde Nemours and Company) or amide-modified polyimide resin (sold underthe trade designation AI by Westinghouse Electric Corporation). Theseresins are described in U.S. Pat. Nos. 3,179,634 and 3,179,635,respectively. As will be apparent to anyone skilled in the art, however,other flexible fire-resistant insulating materialsv which will survivethe failure of the conductor under overload conditions in an oxygenatmosphere, as demonstrated by the NASA test conditions, can also beutilized. Very few such materials are known in the present state of theart. None has been found which survives failure of a copper conductor.By use of a copper-clad aluminum conductor and by keeping the adhesiveout of contact with the conductor, polyimide and amide-modifiedpolyimide film insulations survive the fusion of the conductor onoverload. Thus, any flexible insulation material which resistscombustion at the temperatures to which it is exposed under suchcircumstances would serve equally well.

The thickness of the insulation wrapping should be at least about 0.5mil. Desirably, the wrapping is constituted by two or more layers of 12mils thick polyimide film having a backing ofO. 1-0.5 mil FEP. Thus theinsulation as a whole has a total thickness of 3-l0 mils, depending inpart on the extent of lapping. Greater thicknesses can be utilized butare not normally necessary.

The use of an adhesive material is necessary to seal the insulationwrapping in order to impede electrical current leakage or the access ofeither moisture or oxygen to the conductor. The adhesive material shouldbe flame resistant under normal conditions and should have a softeningpoint of between about 300 F. and about 600 F. If the softening point ofthe adhesive is substantially less than 300 F., it may melt prematurelyon overload and seep past the film insulation into contact with theconductor, thus being exposed to high temperatures and raising thehazard of fire. If the adhesive has a softening point substantiallygreater than 600 F., on the other hand, the mechanical and electricalproperties of the conductor may be adversely affected by the excessivetemperatures required in the process of sealing the insulation with theadhesive. Among the adhesive materials which possess the characteristicsnecessary for use in the cable of this invention may be noted the epoxyadhesive films sold under the trade designations CMC l5 and CMC 16 bythe Circuit Materials Co., the polyester adhesive sold under the tradedesignation 46950 Polyester Adhesive by E. l. DuPont de Nemours andCompany, the polyamide-imide sold under the trade designation TR 150-25by Thermo-Resist, Inc., the silicones sold under the trade designationsSR-585 by the General Electric Company and DC-280 by Dow CorningCorporation, the epoxy sold under the trade designation D.E.N. 438 bythe Dow Chemical Company, the nitrile rubber phenolic sold under thetrade designation Plastilock 605 by the B. F. Goodrich Company, and thefluorinated ethylene propylene resin sold under the trade designationFEP Teflon by E. I. DuPont de Nemours and Company. FEP Teflon is apreferred adhesive since its softening point is at the upper end of the300-600 F. range. It thus has a high degree of stability during thesubjection of the cable to a current overload, without creatinginsuperable problems in the process of applying the insulation to theconductor.

After the tape insulation has been wrapped around the conductor strandsthe adhesive lying between fac ing areas of the insulation is fused toseal said facing layers together. The adhesive is fused by raising it toa temperature at or above its softening point for a period sufficientfor it to form a strong bond to each of the facing areas of the tapebetween which it lies. This operation is conveniently performed in anoven. Where an adhesive having a relatively high softening point such asFEP Teflon" is employed, residence time in the oven is preferably heldto a minimum to avoid adverse effects on the mechanical properties ofthe conductor strands, Exposure to sealing temperatures for excessperiods of time can also result in seepage of the adhesive past the tapeinsulation and into contact with the conductor or can adversely affectthe silver or nickel plating.

A method has been developed for applying the film insulation wrappingand sealing it with the adhesive which assures a high integrity sealwhile protecting the other essential properties of the cable. In thismethod, an insulation tape is used which has a backing of adhesivematerial. The tape is wrapped around the conduc tor with thebacking-facing outwardly. The wrapped cable is then moved continuouslythrough an oven having a temperature profile which is a function of thenature of the adhesive. Thus, the inlet temperature of the furnaceshould not be higher than about 600 F. while the outlet temperatureshould be between the softening point temperature of the adhesive andabout 850 F.

To avoid overheating of the wire with consequent loss of mechanicalproperties and also to avoid seepage of the adhesive or deterioration ofthe outer layer of the composite conductor, the cable is moved throughthe oven at a rate sufficient to raise the adhesive temperature up toits softening point but not substantially above it. Because theconductor strands not only act as a heat sink but through axial heattransfer cause the loss of heat from the furnace, the residence timerequired to bring the adhesive to the desired temperature variesradically with the cross-sectional area of the conductor strandscontained in the cable. Thus for F EP Teflon" adhesive, where the inletoven temperature is 600 10 F. and the exit oven temperature is 850 i 10F it has been determined that the following residence times must bemaintained within i 5 percent to insure a high tion having 19 29-gaugewoven composite metal strands. The copper cladding constituted 15percent by volume of each strand and was coated with a 50 microinchthick layer of silver. Two individual layers of Kapton film insulationtape were helically wound around the woven strands. The inner layer was2 mils thick and had a 0.5 mil thick layer of FEP on its outer side. Theouter layer was 1 mil thick, and had a 0.1 mil thick layer of FEP oneach side. The insulation was sealed by passing the cable through anoven with an inlet temperature of 600 F. and an outlet temperature of850 F. with the residence time in the oven being about 43 seconds.

From the cable thus prepared, a number of lengths of cable samples werecut. From these cable samples, a test bundle was prepared consisting ofseven lengths of cable, six of which were 12 inches in length, and oneof which was 13 inches in length. The bundle was bound together in threeplaces 4 inches apart using lacing tape. The l 3-inch length of cablewas positioned on the exterior of the bundle and had a r-inch length ofinsulation stripped from each of its ends. The lengths of cable whichformed the bundle were located parallel to each other and one end of thebundle was twisted 180 relative to the other end. I

The exposed ends of the l3-inch length of cable were connected to twohorizontally mounted electrical terminals in a test chamber having avolume of 98 l. The chamber included a center support for the cablesample spaced approximately half way between the two electricalconnections. The chamber was also provided with a pressure gauge capableof measuring pressure to an accuracy of i 0.1 psia, an oxygen supply anda window for observing and photographing test results.

The electrical terminals inside the chamber were externally connected toa dc. electrical power supply capable of supplying a 250 amp. steadycurrent.

The test chamber was evacuated to a total pressure of less than 5 torr.Oxygen gas containing less than 5 percent by volume of nitrogen andother inert gases was then introduced into the chamber until thepressure of the chamber reached 6.5 psia. The cable sample bundle wasallowed to soak in the oxygen atmosphere for minutes, and then a currentof 100 amp., amp. below the nominal fusion current, was applied to the13-inch cable by means of the external dc. power source. Twelve secondsfollowing the application of current, the cable failed. No evidence ofcombustion, either smoke, fumes or darkening, was evident either beforeor after cable failure. The sample bundle was removed from the testchamber and examined. By cutting away a portion of the insulation of the13-inch cable, it was determined that fusion of the composite metalconductor strands had taken place and that the conductor strands hadconsequently ruptured, causing an interruption in current.

EXAMPLES 2-12 Additional sample lengths were cut from cable prepared inaccordance with the method described in Example 1. Eleven bundles ofcable samples, each containing six 12-inch lengths and one 13-inchlength,

were prepared and tested according to the method described in Example 1.Each of these samples failed at 100 amp. within the time set forth inTable 111.

TABLE 111 No evidence of combustion was evident, either before or aftercable failure. Examination of the cable showed that fusion and ruptureof the composite metal conductor strands had taken place as in Example1.

No other flexible electrical cable, either commercial or experimental,is known to have passed this test.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above products without departingfrom the scope of the invention, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Nonflammable electrical cable, resistant to combustion under currentoverload conditions in an oxygen atmosphere, comprising a compositemetal strand comprising an aluminum base conductor core, an annularcladding of copper metallurgically bonded to the surface of the aluminumbase core, an annular coating of a metal selected from the groupconsisting of silver, nickel and tin overlying the outside surface ofthe copper cladding, and an outer wrapping of flexible fireresistantinsulating material on said composite strand, said wrapping havingfacing areas with adhesive therebetween for sealing purposes, saidadhesive being entirely out of contact with said composite strand, saidcable being resistant to combustion when subjected to a current overloadin an oxygen atmosphere with said strand being fused and the currentbeing interrupted before ignition of said insulating material oradhesive.

2. A cable as set forth in claim 1 wherein the insulating material isselected from the group consisting of polyimide and amide-modifiedpolyimide film.

3. A cable as set forth in claim 1 wherein said adhesive has a softeningpoint of between about 300 F. and about 600 F.

4. A cable as set forth in claim 1 having a plurality of said strandswithin said wrapping.

5. A cable as set forth in claim 4 wherein the aluminum base core is analloy having an ultimate tensile strength of not less than about 9,000psi, an elongation of not less than about 8 percent, and a conductivityof not less than about 60 percent I.A.C.S.

6. A cable as set forth in claim 5 wherein the aluminum base core isconstituted by an alloy containing between about 0.07 percent and about0.65 percent by weight iron, up to about 0.12 percent by weight silicon,up to about 0.03 percent by weight magnesium, between about 0.01 percentand about 0.03 percent by weight manganese, between about 0.02 percentand about 0.04 percent by weight copper, and between about 0.006 percentand about 0.01 1 percent by weight boron, the balance essentiallyaluminum with no more than 0.001 percent by weight each of titanium,vanadium nickel or chromium.

7. A cable as set forth in claim 6 wherein said adhesive material isfluorinated ethylene propylene resin.

8. A cable as set forth in claim 4 wherein said wrapping has asubstantially uniform thickness of at least about 2 mils.

9. A cable as set forth in claim 4 wherein said wrapping includes atleast two individual layers of helically wrapped polyimide tape.

2. A cable as set forth in claim 1 wherein the insulating material isselected from the group consisting of polyimide and amide-modifiedpolyimide film.
 3. A cable as set forth in claim 1 wherein said adhesivehas a softening point of between about 300* F. and about 600* F.
 4. Acable as set forth in claim 1 having a plurality of said strands withinsaid wrapping.
 5. A cable as set forth in claim 4 wherein the aluminumbase core is an alloy having an ultimate tensile strength of not lessthan about 9,000 psi, an elongation of not less than about 8 percent,and a conductivity of not less than about 60 percent I.A.C.S.
 6. A cableas set forth in claim 5 wherein the aluminum base core is constituted byan alloy containing between about 0.07 percent and about 0.65 percent byweight iron, up to about 0.12 percent by weight silicon, up to about0.03 percent by weight magnesium, between about 0.01 percent and about0.03 percent by weight manganese, between about 0.02 percent and about0.04 percent by weight copper, and between about 0.006 percent and about0.011 percent by weight boron, the balance essentially aluminum with nomore than 0.001 percent by weight each of titanium, vanadium nickel orchromium.
 7. A cable as set forth in claim 6 wherein said adhesivematerial is fluorinated ethylene propylene resin.
 8. A cable as setforth in claim 4 wherein said wrapping has a substantially uniformthickness of at least about 2 mils.
 9. A cable as set forth in claim 4wherein said wrapping includes at least two individual layers ofhelically wrapped polyimide tape.
 10. A cable as set forth in claim 4wherein the strands are woven.